Portable system and method for transferring liquefied gas

ABSTRACT

A portable self-contained system for transferring liquefied gas, such as liquid petroleum gas or anhydrous ammonia, from a source tank (e.g., a railcar) to a receiving tank (e.g., a truck cargo tank), includes a portable platform providing transfer equipment such as a motor powered compressor, operating controls, transfer lines as well as valves and connectors to manage and direct the flow of fluid, and emergency controls such as shut off valves and pull away connectors for safety. A grounding system, safety shower and fire suppression system are also provided. A method for transferring liquefied gas from a source tank to a receiving tank using the portable self-contained transfer system includes steps of positioning the transfer system; establishing liquefied gas line and vapor line connections; pulling vapor from the receiving tank, compressing it and forcing it into the source tank, thereby enabling the pressurized vapor to force liquid from the source tank through a vapor line into the source tank; reconfiguring valves, lines and connections to recover residual liquid and vapors from the nearly emptied source tank; evacuating liquid from the liquid lines; and disconnecting the system.

FIELD OF THE INVENTION

[0001] This invention relates to liquefied gas distribution. More particularly, this invention relates to a portable system for transferring liquefied gas, such as liquefied petroleum gas or anhydrous ammonia, from a tank to another tank, and a method for transferring liquefied gas using such a system.

BACKGROUND

[0002] Liquefied petroleum gas (LPG) and anhydrous ammonia are gaseous at normal atmospheric temperatures and pressures, but are liquefied under moderately higher pressure and/or lower temperature. They are stored and transported in a liquid state because it is far more compact. For example, propane is 240 times more compact as a liquid and butane 270 times more compact. As such, liquefied gases are easily stored and highly portable. In contrast, natural gas (e.g., methane) can only be liquefied at extremely low temperatures (e.g., −160° C.) or high pressures, and is therefore expensive to transport as a liquid, and is mainly transported as a gas in long-distance pipelines.

[0003] LPG is produced from two different sources, naturally occurring LPG produced by fractionators and refinery produced LPG. Naturally occurring LPG is separated from associated gases (i.e., natural gas feedstock) flowing out of oil and gas fields. Refinery produced LPG is produced through the process of crude oil refining. In naturally occurring sources, propane and butane are produced as separate products; but with refinery-produced LPG, they are mostly produced as a propane/butane mixture.

[0004] LPG is typically sold by producers from a primary supply terminal located at or near a petroleum refinery, an LPG extraction plant (in the case of naturally occurring LPG), or a bulk seaboard import terminal. The primary supply terminal normally has bulk storage facilities and fixed (i.e., stationary) truck loading terminals. Additionally, storage facilities and truck loading terminals located closer to certain markets are supplied by pipeline from an extraction plant. LPG is typically trucked by bulk road transports from the primary supply terminals or truck loading terminals to distribution depots where it is stored in above-ground tanks for further distribution to retailers and consumers. Thus the conventional LPG distribution network is dominated by pipelines, fixed truck loading terminals and truck transportation.

[0005] What is needed is a cost-effective, portable, self-contained liquefied gas transfer system for efficiently transferring liquefied gas from one tank to another tank, such as from a railcar to a truck cargo tank. Such a system would help reduce dependence on costly pipelines, expensive fixed truck loading terminals and inefficient long-distance truck transportation by enabling increased use of railroads for efficient distribution. Rail facilities without fixed truck loading terminals would be able to use the portable, self-contained transfer system to efficiently transfer liquefied gas from a railcar to a truck for distribution to retailers and consumers. Such a system would enable suppliers to test new markets without an enormous investment in pipelines or fixed truck loading terminals. Such a system would also enable suppliers to react quickly to propane shortages and spot opportunities during winter months.

[0006] Advantageously, a portable, self-contained transfer system could make railroads, and the many benefits of railroad transportation, a more integral part of liquefied gas distribution networks. Railroads provide an efficient, cost-effective and safe freight service. On average, it is estimated, railroads are three times more fuel efficient than trucks. It is also estimated that for every ton-mile a typical truck emits at least three times more nitrogen oxides and particulates than a conventional locomotive, making rail transportation an environmentally friendlier transportation solution. Extensive use of railroads also helps combat highway congestion while reducing adverse land use and massive highway and pipeline construction costs. Furthermore, railroad safety statistics on transportation of hazardous materials show that railroads experience fewer mishaps than trucks, confirming that rail transportation is the safer alternative.

SUMMARY

[0007] The present invention provides a cost-effective, portable, self-contained transfer system for efficiently transferring liquefied gas from a tank to another tank. A method for transferring liquefied gas using such a system is also provided.

[0008] In general, a system in accordance with a preferred embodiment of the present invention includes a platform providing a portable base, an elevated work area, transfer equipment such as a motor powered compressor, operating controls for operational control, transfer piping and hoses as well as valves and connectors to manage and direct the flow of fluid, and emergency controls such as shut off valves and pull away connectors for safety. Additional components of a preferred embodiment may include a grounding system, a safety shower and a fire suppression system.

[0009] A method for efficiently and safely transferring liquefied gas from a tank (i.e., a “source tank”) to another tank (i.e., a “receiving tank”), such as from a railcar to a truck cargo tank, using a portable self-contained transfer system in accordance with an exemplary embodiment of the present invention generally includes steps of positioning the transfer system next to the source tank and receiving tank; connecting the source and receiving tanks to the system using available transfer lines; pulling vapors from the receiving tank; compressing the vapors and forcing the vapors into the source tank, thereby enabling the pressurized vapors to force liquid from the source tank into the receiving tank. In a preferred implementation, steps for recovering residual vapors and liquids from the source tank using the system, and steps for evacuating liquid from the hoses are also provided. Recovery entails drawing residual vapor from the source tank into the liquid section of the receiving tank. Evacuation entails forcing vapors through liquid lines into a receiving tank. Various safety steps may be included, such as chocking wheels and tires to guard against unintended movement; securing the transfer area by displaying signs and placing traffic cones around it; inspecting transfer lines, valves and connections; establishing a ground; and setting-up a safety shower nearby the transfer system.

[0010] It is therefore an object of the present invention to provide a portable transfer system for efficiently and safely transferring liquefied gas.

[0011] It is another object of the present invention to provide a portable transfer system for efficiently and safely transferring liquefied gas, recovering residual vapors and liquid, and evacuating liquid from lines.

[0012] It is yet another object of the present invention to provide a portable transfer system for efficiently and safely transferring liquefied gas, recovering residual vapors and liquid, and evacuating liquid from lines, where such transfer, recovery and evacuation can be performed in a conventional manner and in accordance with applicable laws and industry standards.

[0013] It is still another object of the present invention to provide a method for efficiently and safely transferring liquefied gas, recovering residual vapors and liquid, and evacuating liquid from lines using a portable transfer system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The foregoing and other objects, features and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where:

[0015]FIG. 1 conceptually depicts a conventional railcar having a tank for transporting LPG and a closed dome for housing valves, a gauge and a thermometer well;

[0016]FIG. 2 conceptually depicts a conventional railcar dome arrangement with an opened dome hatch, revealing valves, a thermometer well and a liquid level gauging device;

[0017]FIGS. 3 and 3A conceptually depict a conventional truck cargo tank for transporting LPG with valves for transferring LPG vapors and liquid;

[0018]FIGS. 4 and 4A conceptually depict a portable system for transferring liquefied gas in accordance with an exemplary embodiment of the present invention;

[0019]FIG. 5 conceptually depicts an exemplary fluid transfer means for use with a system in accordance with an exemplary embodiment of the present invention;

[0020]FIG. 5A conceptually depicts an exemplary four-way valve for use with a system in accordance with an exemplary embodiment of the present invention;

[0021]FIG. 6 is a high-level schematic (not drawn to scale) that conceptually depicts use of an exemplary portable transfer system for transferring liquefied gas, such as LPG or anhydrous ammonia, from a pressurized railcar to a truck cargo tank by creating a vapor pressure differential to force liquefied gas from the railcar to the cargo tank in accordance with an exemplary implementation of the present invention;

[0022]FIG. 7 is a high-level schematic (not drawn to scale) that conceptually depicts use of an exemplary portable transfer system for recovering residual liquefied gas and associated vapors, such as LPG or anhydrous ammonia liquid and vapors, from a railcar by pumping vapors from the railcar into the liquid section of the cargo tank in accordance with an exemplary implementation of the present invention;

[0023]FIG. 8 conceptually depicts an exemplary safety shower for use with a preferred embodiment of the present invention;

[0024]FIG. 9 is a schematic that conceptually depicts a portable system configured to transfer liquefied gas from a source railcar to a truck cargo tank in accordance with an exemplary embodiment of the present invention;

[0025]FIG. 10 is a schematic that conceptually depicts a portable system configured to recover and transfer residual vapors and liquid from a source railcar to a another railcar in accordance with an exemplary embodiment of the present invention;

[0026]FIG. 11 is a schematic that conceptually depicts a portable system configured to evacuate liquid from a line in accordance with an exemplary embodiment of the present invention; and

[0027]FIG. 12 is a flowchart that conceptually illustrates steps of an exemplary method for transferring liquefied gas from a source tank to a receiving tank, using a portable system in accordance with an exemplary embodiment of the present invention.

[0028] The referenced Figures are provided to conceptually illustrate features of the invention. The Figures are not drawn to scale. Objects depicted in the Figures may be larger, taller, shorter, wider, narrower or smaller in relation to other objects depicted in the Figures, without departing from the scope of the present invention.

DETAILED DESCRIPTION

[0029] The present invention may be used for transfers of liquefied gas from a source tank to a receiving tank. The source tank and receiving tank may be standalone tanks or part of a railcar or truck, or some other vehicle, structure or device suitable for storing liquefied gas. Thus, by way of example and not limitation, the present invention may be used for rail to truck, rail to rail, rail to storage tank, truck to truck, truck to rail, truck to storage tank, storage tank to truck, storage tank to rail and storage tank to storage tank transfers. To illustrate an exemplary implementation, without limiting the scope of the present invention, railcar to truck cargo tank transfers are described herein.

[0030] Railroad tank cars move bulk LPG. The tank car or railcar is essentially a large cargo tank on a railcar chassis. Small tank cars may have a capacity of 10,500 gallons, while a large (more typical) tank car may have a capacities as high as 34,500 gallons. In contrast, a typical truck will hold under 10,000 gallons. Thus, multiple trucks are typically required to unload a railcar.

[0031] Railcars typically do not have bottom outlets. Instead, connections and accessories for loading, unloading, sampling and gauging are located within a protective housing called a dome 100 located at or near the top center of the railcar 110, as conceptually illustrated in FIG. 1. A work platform 105 is also typically provided for worker access.

[0032] Referring now to FIG. 2, a railcar dome arrangement is conceptually shown. A pressure relief valve 230 is spring-loaded with a start-to-discharge pressure of approximately 255 or 300 psig, depending on the type of railcar. To measure product temperature and liquid level, a thermometer well 220 and liquid level gauge 225 are provided in the dome 100. Liquid and vapor connections are also provided inside the dome, such as vapor valve 210 and liquid valves 205 and 215. A protective cover (i.e., dome hatch) 130 is hingedly attached to the dome.

[0033] Referring now to FIG. 3, a truck having a cargo tank for transporting LPG is conceptually shown. Like railcars, such trucks typically have pressure relief valves; temperature, pressure and liquid level gauges; liquid and vapor transfer lines and valves; and remote emergency valve controls. Unlike railcars, however, trucks typically do not have the loading and unloading valves at the top of the tank. Instead, loading and unloading valves 305-320 and emergency shut-off switches 360 are typically found at the bottom of the cargo tank, near the back of the truck or at the back end of the tank. Pressure relief valves may be found on the top of the truck tank.

[0034] As used herein, the term “lines” refers to hoses and pipes and combinations thereof. It is understood that suitably shaped pipes may be used instead of hoses, and vice versa, without departing from the scope of the present invention. Pipes and hoses provide conduits for communicating fluid from a source to a destination. Because hoses are flexible, they are preferred for making connections to tanks. However, a suitably shaped pipe or combination of pipes, despite being inflexible, may be used in lieu of a hose. Likewise, a hose, despite its flexibility, may be used in lieu of a particular pipe.

[0035] Also as used herein, the terms “connection” “fluid connection”, “connecting” and “fluidly connecting” with respect to lines refer to direct connections, indirect connections, permanent or fixed connections and releasable connections. Connected lines are capable of fluid communication from one line to the other line. Lines that are directly connected have no other lines or components between them. While lines that are indirectly connected have other lines or components between them; they are deemed “connected” because fluid can be communicated from one line to the other line. Even if a valve is connected between two lines, the lines are deemed “connected” if fluid can be communicated from one line to the other line when the valve is opened. Releasable connections are readily removable, such as manually or using conventional tools. A line that is “releasably” connected is a line having a releasable connection. Permanent or fixed connections are connections that are not intended to be readily removable. Thus, the terms “connection” and “connecting” as used herein cover direct connections, indirect connections, permanent or fixed connections and releasable connections.

[0036] Furthermore, as used herein, a connection is considered “disabled” when it is either disconnected or blocked, such as by one or more valves that have been turned off or set to prevent fluid flow between the connection.

[0037] Referring now to FIG. 4 an exemplary portable system for transferring liquid petroleum gas in accordance with the present invention is conceptually shown. The system includes a base 402 for supporting transfer equipment, plumbing and devices required for functional performance of the system. The exemplary system preferably uses industry standard components, e.g., transfer equipment, piping, valves and connectors, in conformance with applicable laws, codes and standards. These components include upper level vapor and liquid lines with supported hoses, connectors and ball valves, as well as ground level vapor and liquid lines with connectors and ball valves. In the United States, the system should comply with the standards set in NFPA 58—Liquefied Petroleum Gas Code, published by the National Fire Protection Association. Preferably, the connectors are threadedly engageable with tank inlets, most preferably by an acme thread. However, it will be appreciated that the invention is not dependent upon or limited to specific types of components identified herein in connection with an exemplary embodiment. Rather, the system may be effective with other types of components (e.g., connectors, valves, controls and transfer means) as may be known, required and/or available in various parts of the world.

[0038] Advantageously, the system is portable. In a preferred embodiment, a plurality of wheels 404 are attached to the base 402 in a conventional manner to support the system off the ground and to facilitate transportation. A tow bar 406 enables releasable attachment in a conventional manner to a vehicle (not shown) equipped with a towing hitch, thereby facilitating transportation of the system. In an alternative embodiment, the system may be equipped with a means for driving it, including an engine, transmission, drive train, operator controls and braking and steering systems. For example, the system may comprise an LPG transfer vehicle. In another alternative embodiment the system may be designed for being carried to a desired location using a forklift, a flatbed truck or other heavy lifting and positioning machinery known in the art.

[0039] Another advantage is that the exemplary system is self-contained. It includes all of the components required for liquefied gas transfers. Some of the components may be removable or standalone products (e.g., a safety shower, grounding system, safety signs and cones). However, these components may be stored on or releasably attached to the base or the elevated platform of the system, or stored along with the system. While the exemplary system depends upon an external high integrity ground connection, external electrical power and external potable water supply, these dependencies do not diminish the system's self-containment. Such external utilities are commonly available at facilities where liquefied gas transfers are performed.

[0040] A fluid transfer means 410, such as a motor driven compressor, is provided. In a preferred implementation, the fluid transfer means includes an explosion-proof compressor, such as a Corkene vertical compressor by Corken, Inc. of Oklahoma City, Okla. The compressor should be sized to consistently provide a volumetric flow rate sufficient to transfer a desired volume of LPG from a source tank to a receiving tank within a reasonable amount of time. Estimated maximum flow rates for Corken® vertical compressors vary from approximately 50 gpm for a model 91 to 1725 gpm for a model HG601AA. By way of example and not limitation, a Corken® vertical compressor model 691, with an estimated maximum volumetric flow rate of approximately 361 gpm, is considered adequate to safely and efficiently unload a large railcar using a system in accordance with the present invention. Of course, the actual volumetric flow rate will depend upon various factors, including compressor speed (i.e., rpm), plumbing (i.e., union piping, fittings and hoses), the tanks, the product being transferred and its temperature.

[0041] Referring now to FIG. 5A, components of an exemplary fluid transfer means are shown. Compressor 505 is belt driven by motor 510. A liquid trap 515 is provided on the inlet (“suction”) side to prevent liquid from entering the compressor. Preferably, the liquid trap includes a liquid level switch 520 or similar means that will shut off (e.g., block) the intake line to the compressor in the event of excessive liquid level. A vent valve 525 may be provided at the top of the liquid trap head to provide a vacuum breaking vent in case the trap closes and a vacuum develops between the compressor and the trap. A manual drain valve 530 is also provided. Alternatively, floats with electrical float switches or other liquid level switches may be used to stop the compressor in the event of an excessive liquid level and/or to activate a dump valve to drain the excess liquid. A strainer 545 is preferably provided at the inlet of the liquid trap 515 to prevent foreign debris and particles from entering the compressor 505. Inlet and outlet pressure gauges 550 and 555 are also preferably provided. Those skilled in the art will appreciate that these elements are typically included in most LPG transfer compressor systems and the aforementioned fluid transfer means is intended to represent a broad category of systems supporting transfer of liquefied gases such as LPG.

[0042] In an exemplary embodiment, a four-way valve 535 is provided. The valve enables connection of two separate pipes or hoses (i.e., lines). Depending upon the valve position, one such line will be in fluid communication with the inlet (suction) side of the compressor, while the other line will be in fluid communication with the outlet (pressurized) side of the compressor. Referring now to FIG. 5B, a four-way valve in accordance with an exemplary embodiment of the present invention is conceptually illustrated. In position 1, line A is in fluid communication with the inlet (suction) side of the compressor, while line B is in fluid communication with the outlet (pressurized) side of the compressor. In position 2, line B is in fluid communication with the inlet (suction) side of the compressor, while line A is in fluid communication with the outlet (pressurized) side of the compressor.

[0043] Referring again to FIG. 4, pipes and hoses (i.e., lines) 412-418 are provided for fluidly connecting the system to a railcar. Line 416 is a vapor line for a railcar. Line 418 is a liquid line for a railcar. The free end of each line preferably includes conventional couplings 432 and 434 for connection to appropriate railcar valves. If unloading may have to be interrupted from time to time, hoses are preferably equipped with shutoff valves at the railcar and tank truck hose ends so they may be operated as “wet” hoses and disconnected between transfers.

[0044] Safety pull-away couplings 420 and 422 (e.g., Tripod® safety couplers by Precision General, Inc., available from Squibb Taylor, Inc.) are provided to enable safe disconnection in the event the system, a truck or a railcar pulls away. Upon disconnection, valves in pull-away couplings 420 and 422 prevent fluid from passing through the disconnected ends of the lines.

[0045] Cantilevered booms 424 and 426 are provided to support vapor and liquid lines 416 and 418 at a convenient height to facilitate connection with a railcar. The booms preferably pivot about their vertical support members. Thus, a user may position the cantilevered booms 424 and 426 over the dome of an adjacent railcar. Releasable connections 428 and 430 (e.g., Tripin® hose releases by Precision General, Inc., available from Squibb Taylor, Inc.) are provided to allow the hoses to safely disengage from the booms 424 and 426 in the event of a pull away.

[0046] Although lines 416 and 418 are suspended above ground level, the system is not limited to use with a tank having elevated connections (e.g., a railcar having connections on top of its tank). Instead, if the system will transfer liquefied gas from a source tank having ground level connections to another tank having ground level connections, extension hoses may be connected to lines 416 and 418 if necessary to reach the ground connections.

[0047] Lines 452-456 are provided for fluidly connecting the system to a receiving tank (e.g., a cargo tank of a truck, a stationary storage tank or a railcar). Line 456 is a vapor line. Line 454 is a liquid line. The free end of each line preferably includes conventional couplings 458 and 460 for connection to tank valves or connections. If the lines will transfer liquefied gas to a receiving tank having elevated connections, then extension hoses may be connected to liquid lines 454 and 456 if necessary to reach the elevated connections.

[0048] Safety pull-away couplings 462 and 464 (e.g., Tripod® safety couplers by Precision General, Inc., available from Squibb Taylor, Inc.) are provided to enable safe disconnection in the event the system or a vehicle (e.g., a railcar or a truck) pulls away. Upon disconnection, valves in pull-away couplings 462 and 464 prevent fluid from passing through the disconnected ends of the lines.

[0049] An elevated platform 470 with a spring-loaded cantilevered walkway 472 preferably provides access to the work platform and dome of a railcar. The platform 470 and walkway 472 are preferably approximately the same height as the operating platform of a liquefied gas railcar; though other platform heights, such as the height of a truck cargo tank or a platform height between the height of a truck cargo tank and the height of a railcar may be used. A staircase 474 or a ladder provides access to the elevated platform 470. When extended, the walkway 472 provides a bridge for safely crossing from the platform 470 to an operating platform of a liquefied gas railcar and/or to the top of a truck. In a conventional manner, springs preferably prevent the walkway from striking the work platform with excessive force. In a preferred embodiment, the walkway is comprised of a non-ferrous material, e.g., aluminum, to reduce the risk of sparking when it contacts the work platform.

[0050] The elevated platform and walkway provide important advantages. These features facilitate access to the dome of a railcar tank. These features also facilitate access to the top of truck cargo tanks and stationary storage tanks, where pressure relief valves may be located.

[0051] People skilled in the art will appreciate that alternative elevated platforms means may be used without departing from the scope of the present invention. For example, a platform capable of being elevated using hydraulics or other elevation means comes within the scope of the present invention.

[0052] Although having an elevated platform is preferred, those skilled in the art will also appreciate that a portable system without an elevated platform also comes within the scope of the present invention. In such case, the booms, stairway, walkway and associated components may be eliminated without departing from the scope of the present invention.

[0053] Safety is an important concern in transferring liquefied gases. Especially in the case of LPG, which is nearly twice as heavy as air, gas leaks could spread a considerable distance before a gas is diluted by air below explosive and flammable concentrations. Safety components preferably enable an operator to quickly shutdown the system to help minimize the potential volume and duration of an accidental release and to terminate a transfer operation in the event of a fire or other emergency.

[0054] A system in accordance with the present invention preferably includes various safety components, such as means for remote and automatically closing valves; interlocks to main system control and the power supply; alarms; a fire suppressant and a safety shower. Such devices can help achieve a controlled, safe shutdown and improved emergency response.

[0055] Preferably, the system includes a plurality of emergency shutoff valves. A source tank adapter with an emergency shutoff valve is preferably installed between the liquid unloading hose and the source tank liquid valves. Another emergency shutoff valve is preferably installed in rigid vapor piping on the transfer system side of the vapor hose. Another source tank adapter with an emergency shutoff valve is preferably located between the vapor hose and the source tank vapor valve. Another emergency shutoff valve is preferably installed in rigid vapor piping on the portable transfer system side of the vapor hose.

[0056] All emergency shutoff valves are preferably equipped for manual shutoff, thermal release, and remote operation. Remote emergency shutdown controls should be located where they can be reached safely in an emergency. In a preferred embodiment, the portable transfer system has a local emergency shutdown switch located on a main electrical panel and a remote emergency shutdown switch on a portable stand which may be placed a safe but easy to reach distance (e.g., 50 feet) from the portable transfer system.

[0057] Suitable emergency shutoff valves and controls are known in the art. By way of example and not limitation, a suitable emergency shutoff valve designed for attachment to shutoff valves on railcars is the Fisher® N560 Series Emergency Shutoff Valve by Fisher Controls International, Inc. Approximately 20 to 60 psig (1.4 to 4.1 bar) of pressurized gas is needed to open the valve, depending upon tank car pressure. Remote closure is accomplished by exhausting pressure from the valve's piston chamber with a pneumatic control valve. Preferably the pneumatic pressure required to open the valve is provided from a source of compressed nitrogen (N₂) gas. Thermal release means is also provided. A fire will compromise a plastic connector for the pressurized nitrogen supply, causing a pressure release and closure of the valve.

[0058] An exemplary emergency shutoff valve designed for in-line installation is the Fisher® N550 Series Emergency Shutoff Valve by Fisher Controls International, Inc. It can be manually opened and closed at the installed location, or closed remotely by either cable or pneumatically. A remote operating actuator is available from the manufacturer. Pneumatic pressure (preferably compressed nitrogen (N₂) gas at 30 to 70 psig [2.7 to 4.8 bar]) allows the valve to be latched in the open position with manual closure possible at the valve. Loss of pressure causes closure. Thermal release means is also provided. A fire will compromise a plastic connector for the pressurized nitrogen supply, causing a pressure release and closure of the valve.

[0059] The risk of static build-up, sufficient to create a spark causing explosions, costly fires, property damage and injury to personnel is a constant danger in LPG transfer operations. To drain off static charges, a grounding system should be used (e.g., the Scully Groundhog™ Vehicle Static Grounding System by Scully Signal Company of Wilmington, Mass.). Such systems typically include clamps and cables to establish a connection to a high integrity ground point. In a preferred implementation, conventional grounded and bonded railroad track serves as the high integrity ground point. If a terminal does not have a track that is grounded and bonded, then ground electrodes can be installed, connections should be made between ground electrodes and rails, and bonding should be made between rail sections to achieve grounding and bonding in accordance with applicable laws and industry standards before unloading operations commence. Alternatively, another high integrity ground point can be established without departing from the scope of the present invention.

[0060] In addition to establishing the ground connection, the preferred grounding system also preferably provides a visual confirmation (e.g., a green light to indicate a proper ground and a red light to indicate an improper ground). The grounding system may also provide operational confirmation through interlocks on the pump, valves, motor or control interfaces. The system may also provide a resistance check and capacitance check to confirm proper unit connection. Preferably, the source tank, receiving tank and portable system should be grounded before loading or unloading can take place.

[0061] Operating controls are preferably provided at strategic locations on the system. The locations should facilitate normal operation and emergency shutdown. For example, elevated and ground level operation and emergency shutdown controls are preferably provided. A remote shutdown switch (as discussed above) is also preferably provided.

[0062] An exemplary system in accordance with the present invention preferably also includes a portable safety shower, as conceptually shown in FIG. 8. The safety shower preferably includes a shower head 805, a shower pull 810, an eyewash/facewash sink 815, a support base 820, plumbing and a water heater (preferably a tankless water heater) 830. Potable water may be supplied to connection 835 from a hose, another plumbing connection or a tank (e.g., an air pressurized water tank). Preferably, the portable safety shower and its location relative to the transfer system conform with applicable laws and standards, such as The American National Standards Institute's standard on this subject designated ANSI Z358.1-1990, entitled American National Standard for Emergency Eyewash and Shower Equipment. An exemplary system in accordance with the present invention preferably also includes a fire suppression means, such as at least one twenty-pound (20-lb.) portable ABC class fire extinguisher releasably mounted on the system. Additional extinguishers as well as other fire suppression means may also be utilized. The fire suppression means, its attachment and location relative to the transfer system should conform with applicable laws and standards, such as the American National Fire Protection Association's standard NFPA 58, entitled Liquefied Petroleum Gas Code.

[0063] A system in accordance with a preferred embodiment of the present invention creates a pressure differential to force liquefied gas from a source tank (e.g., a railcar) 605 to a receiving tank (e.g., a cargo tank) 610 of a truck, as conceptually illustrated in FIG. 6. In operation, a piping connection 615 is made from the outlet (high-pressure side) of the compressor 630 to the top of the vapor section of the railcar tank. Another connection 620 is made from the inlet (suction side) of the compressor 630 to the top of the vapor section of the truck cargo tank. A piping connection 625 is also made between the liquid sections of the two tanks. The compressor 630 creates a pressure differential by drawing gas from the top of the vapor section of the truck cargo tank, thereby lowering the cargo tank pressure, and forcing gas into the top of the railcar tank, thereby increasing railcar tank pressure. When the pressure in the railcar tank is increased enough to overcome pipe friction and any static elevation difference between the tanks, liquid is forced from the railcar tank 605 through eduction tubes (i.e., liquid dip tubes) in the tank, through the liquid piping 625 and into the cargo tank 610.

[0064] An advantage of using a compressor instead of a liquid pump as a transfer means is that a compressor may recover valuable residual vapors, while a liquid pump cannot. After most of the liquid has been transferred from the railcar 605 using vapor differential pressure as described above, some valuable liquid and vapors remain. To remove remaining liquid and residual vapors, the direction of flow through the compressor 630 is reversed by means of the compressor four-way control valve (described above). A vapor line connection 715 is established from the inlet (suction side) of the compressor 630 to the top of the vapor section of the railcar tank 605. Another vapor line connection 720 is made from the outlet (high-pressure side) of the compressor to the liquid section of the truck cargo tank 610. The liquid connection 625 between the liquid sections of the tanks may either be closed or removed.

[0065] To recover residual vapors, the compressor 630 draws gas from the top of the vapor section of the railcar tank 605, thereby lowering the railcar tank 605 pressure. The drop in pressure causes remaining liquefied gas to vaporize and the vapors are drawn from the top of the railcar. Recovered vapors are discharged into the cargo tank 610 liquid section (i.e., bubbled through the liquid) where they cool and condense. If the recovered vapors do not condense, the cargo tank can develop an excessive pressure. After all or most of the liquid has been vaporized, the compressor may continue to draw gas from the tank car until the tank car pressure is reduced to an economical point (e.g., a point at which the cost of operation does not exceed the value of the recovered product). By way of example and not limitation, it is estimated that an economical limit is attained when the pressure of a large railcar reaches approximately 50 psig, as determined from the compressor inlet gauge. Thus, recovery below that pressure might not be considered economical.

[0066]FIG. 9 is a schematic conceptually depicting components of an exemplary portable system for transferring liquefied gas in accordance with the present invention. Compressed nitrogen supply tank 904 supplies nitrogen to shutoff valves 909, 910, 911, 918, 919, 931 and 932, via lines 953 through 958. A remote emergency shutdown station 902 with a control panel 901 enables opening of remotely activated solenoid valve 903. When opened, remotely activated solenoid valve 903 allows supplied nitrogen gas to escape, thereby relieving pressure to nitrogen-supplied shutoff valves 909, 910, 911, 918, 919, 931 and 932 and causing the valves to close.

[0067] A ground system 906 establishes grounds with the railcar frame 907, the truck frame 908 and the portable transfer system 990, via conductive cables 951, 952 and 991 equipped with conventional grounding clamps. Grounded and bonded railroad track, which is in conductive communication with the railcar frame, provides a high integrity ground point.

[0068] Pullaway connectors are provided at 912, 913, 914 and 915. Acme (threaded) connectors are provided at 920 and 922 to establish liquid and vapor line connections at the railcar dome. Acme (threaded) connectors are also provided at 939 and 940 to establish liquid and vapor line connections at the cargo tank.

[0069] Vapor lines 964 and 965 enable fluid communication of gas from the high pressure side of the compressor 928 to the railcar tank. Vapor line 963 enables fluid communication of gas from the cargo tank to the low pressure (suction) side of the compressor 928. Liquid lines 960 through 962 enable fluid communication of liquid from the railcar tank to the cargo tank.

[0070] As discussed above, the preferred fluid transfer means includes a motor 929, a compressor 928, a strainer 927 and a liquid trap 926. Conventional vapor pressure sensors and/or gauges 923 and 924 are also provided to detect low and high pressures. Additionally, a conventional oil pressure sensor 925 is preferably provided for the compressor.

[0071] A safety shower 970 includes a shower head 971, a shower pull 972, an eyewash/facewash sink 973, a support base 974, and plumbing. Potable water may be supplied to a field connector 975.

[0072]FIG. 10 is another schematic conceptually depicting components of an exemplary portable system for transferring liquefied gas in accordance with the present invention. In FIG. 10, the system is configured for vapor recovery. Thus, liquid lines are not used. Vapor is drawn from a tank 1001 with residual vapors and liquid, through the compressor 928 and into a tank to be filled 1002, via vapor lines 1003 and 1004.

[0073]FIG. 11 is another schematic conceptually depicting components of an exemplary portable system for transferring liquefied gas in accordance with the present invention. In FIG. 11, the system is configured for liquid hose evacuation. Vapor is drawn from a tank 1001 with residual vapors, through a vapor hose 1102, through the compressor 928, and forced through a liquid hose evacuation manifold 1005, into a liquid line 1105 to be evacuated and finally into a tank to receive the liquid and vapors 1002.

[0074] Though FIGS. 6 and 7 and 9 through 11 illustrate use of the system with two railcars or with a railcar and a truck, those skilled in the art will appreciate that a portable transfer system in accordance with the present invention is not limited to use with a specific combination of tanks or vehicles, provided that the source tank and receiving tank are capable of receiving and storing the liquefied gas.

[0075] Referring now to FIG. 12, a flowchart is provided to conceptually illustrate steps of a method of using an exemplary portable system for transferring liquefied gas in accordance with the present invention. Transfer procedures may differ depending upon the particular configuration of a portable transfer system, the tanks/vehicles between which the liquefied gas is being transferred, the type of liquefied gas being transferred and the facilities. All transfers should be performed in accordance with applicable laws, equipment specifications and industry standards. Only persons familiar with all equipment and properly instructed in applicable laws and safety and transfer procedures should perform the transfer. A qualified person should be in attendance during an entire period a railcar is connected.

[0076] An initial step entails positioning the portable transfer system 1210. The system may be towed, pushed, carried or otherwise moved to a desired location and orientation. Preferably, the system is located adjacent to the tanks between which liquefied gas will be transferred. For example, if the source tank is a railcar, the system should be positioned beside the source railcar so the walkway can be lowered into a position providing a safe walking surface from the platform to the railcar. The transfer platform should then be secured (e.g., wheels chocked) to prevent unintended motion.

[0077] Safety and administrative steps should be performed 1220. Such steps may include inspecting the tanks, components and equipment; securing the work area; erecting caution signs; establishing ground connections; checking the amount and properties of the liquefied gas and compressed nitrogen; ensuring that brakes are set; and chocking wheels.

[0078] Next, railcar connections are made 1230. After accessing and opening the dome, the operator should check all railcar valves and fittings for leaks or damage that would prevent safe use. After checking for leaks, the operator should remove a plug from the sampling valve and slowly open the valve slightly to check for odorant in the gas. LPG in its pure component form is odorless. To make it easily detectable when leaking, producers add a compound such as mercaptan sulphur in such concentration to impart a readily detectable foul smell even at low levels. LPG should not be unloaded if odorant is not detected. If odorant is detected, the operator should make a note of it. After checking for odorant, the operator should check and record the temperature of the liquid contents by inserting an armored thermometer into the well. Liquid level should also be determined and recorded using a level gauge in a conventional manner. Of course, if the reading reveals an appreciable shortage of liquefied gas, appropriate parties should be notified and further inspection may be warranted.

[0079] After checking the temperature and liquid level, the operator should install adapters, emergency shutdown valves and hoses. Railcar adapters may be installed into the liquid and vapor valves. Emergency shutdown valves may be installed to liquid and vapor railcar adapters. The integrity of all connections and hoses should be inspected. Assuming the inspection reveals no defects, the operator may install liquid and vapor hoses to the source tank. In the case of a railcar source tank, hose support arms (i.e., booms) can be pivoted into position to connect the railcar liquid and vapor hoses to the liquid and vapor connections. Nitrogen lines should also be connected to emergency shutdown valves. After connecting hoses, source tank liquid and vapor valves may be opened to test for leaks. If any leaks are detected, the valves should be closed and the leak fixed. If there are no leaks or after all leaks have been corrected, the valves should be opened fully.

[0080] Next, receiving tank (e.g., cargo tank) connections are made 1240, preferably in a safe and orderly manner similar to that described above for establishing source tank connections. The transfer system's liquid line should be connected to the receiving tank's fill valve and the transfer unit's vapor return line should be connected to the receiving tank's vapor valve.

[0081] To initiate pressure differential transfer 1250, the four-way valve on the compressor should be adjusted so the direction of vapor flow will be from the receiving tank to the source tank. The compressor will pull vapor from the receiving tank through the compressor and then force it into the source tank, increasing the pressure in the source tank. The increased vapor pressure forces liquid in the source tank out through the liquid valves, through the piping network and the liquid hose connected to the receiving tank and into the receiving tank. In a railcar, the increased vapor pressure forces liquid in the source tank up through eduction tubes (liquid dip tubes) out through the liquid valves, through the piping network and the liquid hose connected to the receiving tank and into the receiving tank. When the receiving tank is filled to a determined amount or if the source tank becomes empty of liquid (e.g., as revealed by only vapor passing by the sight flow indicator), the compressor and valves should be closed.

[0082] After completing pressure differential transfer, vapor recovery steps 1260 may be performed if warranted 1255. For example, if the source railcar is nearly empty, i.e., contains a residual “heel” of liquefied gas and vapors, and the cargo tank is not filled to a determined limit, then, vapor recovery may be warranted. In contrast, if the railcar contains a substantial amount of liquefied gas and vapors, e.g., enough to service another truck, vapor recovery may be unwarranted.

[0083] Vapor recovery entails reversing the compressor and pulling vapor from the empty (or nearly empty) source tank, passing it through the compressor, into the liquid hose connected to the receiving tank and into the liquid section of the receiving tank, where the compressed vapors will cool and condense. The 4-way valve should be set so the direction of flow will be from the empty source tank to the receiving tank. Connections, valves and lines should be configured for vapor recovery as described above. The compressor should be operated to pull vapor from the source tank until the vapor has been sufficiently recovered (e.g., until an empty railcar reaches 50 psig), which may be determined by observing the compressor inlet pressure gauge. When the determined point has been reached, the compressor should be stopped.

[0084] Transfer system hoses should be emptied of all liquid before being disconnected. Evacuation entails pulling vapor from a source tank, passing it through the compressor, into the liquid hose, then into the receiving tank. Compressed vapor should be circulated through the liquid line to be evacuated until the liquid is removed. Upon removal of the liquid, the tank vapor valve may be closed and the vapor evacuated from the vapor lines until the inlet pressure of the compressor reaches a determined point (e.g., 35 psig).

[0085] After evacuation, the system may be disconnected 1280. Valves should be shut and hoses and adapters should be disconnected and plugged. After any excess vapor pressure in a hose is bled off, the hose may be capped. Nitrogen should be shut off and disconnected. The electrical supply should be disconnected. The safety shower should be disconnected. All equipment should be stored. The dome sampling valve, thermometer well, gauging device, housing and dome cover should be properly secured. The walkway should be returned to its storage position and the portable transfer system may be stored away.

[0086] The foregoing detailed description of particular preferred embodiments and implementations of the present invention, which should be read in conjunction with the accompanying drawings, is not intended to limit the enumerated claims, but to serve as particular examples of the claimed invention. Those skilled in the art should appreciate that they can readily use the concepts and specific embodiments and implementations disclosed as bases for modifying or designing other systems and methods for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent systems and methods do not depart from the spirit and scope of the invention as claimed. 

Having thus described the present invention, what is claimed as new and desired to be secured by Letters Patent is as follows:
 1. A system for transferring liquefied gas from a source tank to a receiving tank, said system including: a portable platform and liquefied gas transfer means.
 2. A system according to claim I further including a plurality of rotatable wheels functionally connected to the portable platform to facilitate transportation.
 3. A system according to claim 2 further comprising means for towing the portable platform.
 4. A system according to claim 3 wherein the means for towing includes a tow bar, said tow bar having a first end and a second end, the first end being functionally connected to the portable platform to facilitate towing, the second end having means for releasable attachment to a vehicle for towing.
 5. A system according to claim 1 further including an elevated platform attached to the portable platform, said elevated platform having a height above ground level.
 6. A system according to claim 5 further including means for accessing the elevated platform.
 7. A system according to claim 6, wherein the means for accessing the elevated platform includes climbing means from the group consisting of a stairway and a ladder.
 8. A system according to claim 5 further including a walkway for accessing the top of a nearby tank having a height that is the same as or close to the height of the elevated platform.
 9. A system according to claim 8 further including hinged attachment means for attaching the walkway to the elevated platform.
 10. A system according to claim 9 wherein the walkway further includes means for folding the walkway to facilitate storage.
 11. A system according to claim 8 wherein the walkway is comprised of a material that is not likely to generate sparks upon contacting the nearby tank.
 12. A system according to claim 11 wherein the walkway is comprised of aluminum.
 13. A system according to claim 5 further including an elevated vapor hose fluidly connected to the liquefied gas transfer means, an elevated liquid hose, a first boom and a second boom, a plurality of releasable boom attachment means for releasably attaching the elevated vapor and liquid hoses to the first and second booms, the first boom and second boom being functionally attached to the elevated platform, the elevated vapor hose being releasably attached to the first boom using a releasable boom attachment means, and the elevated liquid hose being releasably attached to the second boom using a releasable boom attachment means.
 14. A system according to claim 13 wherein the first boom is pivotable about a first vertical axis to facilitate positioning of the boom, and the second boom is pivotable about a second vertical axis to facilitate positioning of the boom.
 15. A system according to claim 13 further including a first pullaway connector functionally connected to the elevated vapor hose and a second pullaway connector functionally connected to the elevated liquid hose.
 16. A system according to claim 13 further including a first emergency shutoff valve functionally connected to the elevated vapor hose and a second emergency shutoff valve functionally connected to the elevated liquid hose.
 17. A system according to claim 16 further including a platform level vapor hose fluidly connected to the liquefied gas transfer means, and a platform level liquid hose fluidly connected to the elevated liquid hose.
 18. A system according to claim 17 further including a third pullaway connector functionally connected to the platform level vapor hose and fourth pullaway connector functionally connected to the platform level liquid hose.
 19. A system according to claim 18 further including a third emergency shutoff valve functionally connected to the platform level vapor hose and a fourth emergency shutoff valve functionally connected to the platform level liquid hose.
 20. A system according to claim 19 further including an emergency shutoff means for shutting off the first, second, third and fourth emergency shutoff valves.
 21. A system according to claim 20 wherein the emergency shutoff means includes an emergency shutoff switch located at or near the platform, an emergency shutoff switch located at or near the elevated platform and an emergency shutoff switch located a determined distance from the platform.
 22. A system according to claim 1 further including a grounding means for grounding the source and receiving tanks.
 23. A system according to claim 22 wherein the grounding means includes a portable grounding system.
 24. A system according to claim 1 further including a safety shower.
 25. A system according to claim 24 wherein the safety shower is a portable safety shower.
 26. A system according to claim 1 further including fire suppression means.
 27. A system according to claim 26 wherein the fire suppression means includes an ABC class fire extinguisher releasably attached to the system.
 28. A system according to claim 1 wherein the liquefied gas transfer means includes a compressor having an outlet and an inlet.
 29. A system according to claim 28 further including a control valve fluidly connected to the inlet of the compressor and to the outlet of the compressor, said control valve having a first line connection and a second line connection each of which may be used for connecting a line to the control valve, said control valve also having a first setting that fluidly connects the first line connection to the inlet of the compressor and the second line connection to the outlet of the compressor, and a second setting that fluidly connects the second line connection to the inlet of the compressor and the first line connection to the outlet of the compressor.
 30. A system according to claim 29 further including: a first vapor hose having a first end and a second end, the first end being fluidly connected to the first line connection of the control valve, a first liquid hose having a first end and a second end, a second vapor hose having a first end and a second end, the first end being fluidly connected to the second line connection of the control valve, and a second liquid hose having a first end and a second end.
 31. A system according to claim 30 further including: a first pullaway connector functionally connected to the first vapor hose and a second pullaway connector functionally connected to the first liquid hose, a first emergency shutoff valve functionally connected to the first vapor hose and a second emergency shutoff valve functionally connected to the first liquid hose, a third pullaway connector functionally connected to the second vapor hose and fourth pullaway connector functionally connected to the second liquid hose, and a third emergency shutoff valve functionally connected to the second vapor hose and a fourth emergency shutoff valve functionally connected to the second liquid hose.
 32. A system according to claim 31 further including: an emergency shutoff means for shutting off the first, second, third and fourth emergency shutoff valves, wherein the emergency shutoff means includes an emergency shutoff switch located at or near the platform and an emergency shutoff switch located a determined distance from the platform.
 33. A system according to claim 32 further including a portable grounding means for grounding the source and receiving tanks.
 34. A system according to claim 33 further including a portable safety shower.
 35. A system according to claim 34 further including a fire suppression means, wherein the fire suppression means includes an ABC class fire extinguisher releasably attached to the system.
 36. A system according to claim 35 further including a means for towing the portable platform, the means for towing including a tow bar, said tow bar having a first end and a second end, the first end being functionally connected to the portable platform to facilitate towing, the second end having means for releasable attachment to a vehicle for towing.
 38. A method for transferring liquefied gas from a source tank having liquefied gas and vapors to a receiving tank having vapors using a system according to claim 1, said method including steps of positioning the system to perform the transfer, fluidly connecting the liquefied gas transfer means to the receiving tank to enable the liquid transfer means to draw vapors from the receiving tank, fluidly connecting the liquefied gas transfer means to the source tank to enable the liquid transfer means to pump compressed vapors drawn from the receiving tank into the source tank, thereby increasing the vapor pressure in the source tank, fluidly connecting the source tank to the receiving tank to enable liquefied gas to flow from the source tank to the receiving tank, operating the liquefied gas transfer means to draw vapors from the receiving tank through the liquefied gas transfer means and into the source tank, thereby increasing the vapor pressure in the source tank and forcing liquefied gas from the source tank into the receiving tank.
 39. A method according to claim 38 further including steps of disabling the fluid connections established according to claim 35, thereby preventing liquefied gas from flowing from the source tank into the receiving tank, and preventing vapors from being drawn from the receiving tank and pumped into the source tank, fluidly connecting the liquefied gas transfer means to the source tank to enable the liquid transfer means to draw vapors from the receiving tank, fluidly connecting the liquefied gas transfer means to the receiving tank to enable the liquid transfer means to pump compressed vapors drawn from the source tank into liquefied gas that was forced into the receiving tank according to claim 38, and operating the liquefied gas transfer means to draw vapors from the source tank through the liquefied gas transfer means and into the liquefied gas contained in the receiving tank, thereby decreasing vapor pressure in the source tank and promoting evaporation of liquefied gas in the source tank, and enabling all or some of said compressed vapors to cool and condense in the liquefied gas of the receiving tank.
 40. A method for transferring liquefied gas and vapors from a source tank having liquefied gas and vapors to a receiving tank having vapors using a system according to claim 30, said method including steps of positioning the system to perform the transfer, fluidly connecting the second end of the first vapor hose to the source tank, fluidly connecting the first end of the first liquid hose to the first end of the second liquid hose, fluidly connecting the second end of the first liquid hose to the source tank, fluidly connecting the second end of the second vapor hose to the receiving tank, fluidly connecting the second end of the second liquid hose to the receiving tank, setting the control valve such that the first line connection, which is connected to the first end of the first vapor hose, is fluidly connected to the outlet of the compressor and the second line connection, which is connected to the first end of the second vapor hose, is fluidly connected to the inlet of the compressor, and operating the liquefied gas transfer means to draw vapors from the receiving tank, through the second vapor hose, into the liquefied gas transfer means, through the first vapor hose and then into the source tank, thereby increasing the source tank's vapor pressure to force liquefied gas from the source tank, through the first liquid hose, into the second liquid hose, and then into the receiving tank.
 41. A method according to claim 40 further comprising steps of disabling at least one of the following connections: the connection between the first end of the first liquid hose and the first end of the second liquid hose, the connection between the second end of the first liquid hose and the source tank, and the connection between the second end of the second liquid hose and the receiving tank, and setting the control valve such that the first line connection, which is connected to the first end of the first vapor hose, is fluidly connected to the inlet of the compressor and the second line connection, which is connected to the first end of the second vapor hose, is fluidly connected to the outlet of the compressor, and operating the liquefied gas transfer means to draw vapors from the source tank, through the first vapor hose, into the liquefied gas transfer means, through the second vapor hose and into the liquefied gas contained in the receiving tank, thereby decreasing vapor pressure in the source tank and promoting evaporation of liquefied gas in the source tank, and enabling all or some of said compressed vapors to cool and condense in the liquefied gas of the receiving tank.
 42. A method according to claim 41 further comprising steps of evacuating liquefied gas from the first liquefied gas hose, and evacuating liquefied gas from the second liquefied gas hose.
 43. A method for transferring liquefied gas and vapors from a source tank to a receiving tank using a system according to claim 1, said method including steps of positioning the system to perform the transfer, establishing a vapor line connection from the source tank to the liquefied gas transfer means, establishing a vapor line connection from the receiving tank to the liquefied gas transfer means, establishing a liquefied gas line connection from the source tank to the receiving tank, operating the liquefied gas transfer means to draw vapors from the receiving tank, through vapor line connection from the receiving tank to the liquefied gas transfer means, through the vapor line connection from the source tank and then into the source tank, thereby increasing the source tank's vapor pressure to force liquefied gas from the source tank, through the liquefied gas line connection from the source tank to the receiving tank, into the receiving tank.
 44. A method according to claim 43 further comprising the step of recovering vapors from the source tank into the liquefied gas transferred into the receiving tank.
 45. A method according to claim 44 further comprising the step of evacuating liquefied gas from the liquefied gas line connection from the source tank to the receiving tank. 